I suppose no-one, anywhere, has direct human experience of the nature of solid CO2 that's frozen out of the atmosphere onto a landscape. Whilst it's behaviour is obviously very well characterised in a laboratory setting, I'd be surprised if there were no surprising features at all observed during whatever part of the early depostiion process we're lucky enough to witness before Phoenix's final transmission.

I'm no chemist, but ISTR water has some very unusual properties (the solid being less dense than the liquid form, for instance), due to some unique features of the electron bonds between the atoms in the molecule. (Apologies to the experts whose heads just exploded.) CO2 doesn't have those features, so I suspect the behaviour of CO2 ice freezing out onto a spacecraft will be fairly unintuitive when those tuits derive from our collective experience of the behaviour of water ice. (Statement of the bleedin' obvious, I know... sorry )

I'm guessing that the CO2 deposition would start on the coldest exposed surface - assuming negligable heat transfer across the metal of the spacecraft, I would guess that the coldest surface would be the shaded part of the exposed solar panels. And so as winter approached, CO2 deposition would occur on the windward side of the shaded part of the solar panels.

So actually, the last part to get covered in CO2 deposit should be the sunlight-exposed part of the black solar panels.

[And on a lucky day, maybe the underside CO2 deposit will hook up with the CO2 deposit growing upward from the ground and not cause the solar panels to snap with all the weight.]

Either way, I'm hoping the imaging part of the mission lasts long enough to start seeing some of these bizarre effects.

-Mike

But frost deposition would start at night, and at night the upwards-facing surfaces will be coldest, since they can radiate into the sky, and the underside of the solar panels will be warmed by the ground as it radiates overnight.

I'm assuming that the transfer of heat by air movement (even though it's really, really low pressure) would be larger than radiative transfer if thermal energy from the ground to the solar panel.

-Mike

Thanks for the correction Greg. Either way, if there is ice on the solar panels thick enough to snap them off, it seems probable to me that the ice would have limited the photovoltaics to negligible levels, rendering the lander dead anyway - providing the sun will even be above the horizon long enough by that time to generate sufficient power.

If only it had an RTG...

Ken

There's one phenomenon we're all forgetting, here. And it surely impacts the possibility of Phoenix's survival upon spring thaw.

You see, as has been noted, the solar panels absorb light. They're very dark. I'd bet you anything that they re-rediate in the infrared -- i.e., like most dark things, they warm up in sunlight more than light things do.

We *know* what happens in the Martian polar spring when the dry ice thins and dark soil or rock patches heat up underneath their icy coatings. The dry ice sublimates from underneath, building up pressure pockets that set up violent structural failures of the covering dry ice layers. That process creates geyser-like dust plumes that have been imaged many times.

During the spring thaw, the dry ice covering the solar panels will warm up and sublimate into gas next to the dark portions of the solar panels.

I'd say it's possible, if not probable, that Phoenix's solar panels will be the scene of local gas-escape explosions in the coming spring.

I'll be *real* interested in seeing what HiRISE shows after a full winter cycle.

-the other Doug

Thar she blows!

Well, seems we just found out that Phoenix is sitting on top of a limitless supply of rocket fuel...

Hmmm... I asked about the possibilities of using the arm to prop the lander up, it apparently doesn't have enough power for that. But they did confirm that it has enough power to drag the lander, if everything was maxed out and it was on a slope...